1. Field of the Invention
The present invention relates to a technology for controlling speed of a magnetic motor.
2. Related Art
As a technology for driving a magnetic motor in a high rotation speed range, Japanese Patent Application Laid-open No. 2005-033957 describes a protective control method of calculating a voltage saturation rate standing for a degree of voltage saturation, from an input voltage inputted to a power converter for driving the magnetic motor and a commanded voltage value given to the magnetic motor and of lowering a target rotation speed value given from the outside until when the voltage saturation rate becomes smaller than a voltage saturation rate preset value.
On the other hand, this method described in JPA 2005-033957 has a problem which results from its control principle, the problem that the maximum use can not be made of the voltage saturation rate because this method requires the voltage saturation rate to be set smaller than the preset voltage saturation rate value.
That is, this method has a problem that the maximum voltage of the power converter cannot be applied to the motor and as a consequence, the maximum use can not be made of the upper limit torque of the motor.